The method of parenteral administration is known to be useful in helping the absorption of many drugs and, among them, also of the non-steroidal anti-inflammatory drugs.
The sodium salt of naproxen, among these, a drug universally known for its valued analgesic, antipyretic and anti-inflammatory activities, has a remarkable importance.
The possibility to use the sodium salt of the naproxen for injectable use was limited till now by the poor stability to heat and light of its aqueous solutions.
As a matter of fact, aqueous solutions containing the sodium salt of the naproxen undergo a quick and strong degradation fostered by light and heat, as fully documented by Douglas E. Moore et al. in Photochem. Photobiol., 47, 173-180, (1988).
Really, till now the use of the naproxen by injectable way was always carried out by dissolving the freeze-dried sodium salt of the naproxen, at the moment of use, by means of a vial containing the solvent liquid.
This kind of preparation and use obviously has many drawbacks, the main of them being the risk of ambient contamination during the dissolution. Therefore it is certainly desirable to have available a single vial, containing the sodium salt of the naproxen already dissolved, which offers remarkable advantages like a greater ease of manufacture and a lowering of the operations necessary for the administration of the drug that brings to an easier use and therefore to lower risks of contamination.
Therefore the object of the present invention consists in finding a system to make stable for a long period of time aqueous solutions containing the sodium salt of the naproxen also in the presence of unfavourable conditions of heat and light.
We discovered that by adding antioxidizing and radical scavanger chemical substances like, for instance, compounds containing sulphydryl, sulfide or disulfide groups, together with polyhydroxylic alcohols, to the aqueous solutions of the sodium salt of the naproxen, the stability of these aqueous solutions increases in a very remarkable manner. This stability becomes further more marked by packaging the vials or the medicine-bottles containing these stabylized solutions in suitable containers made by boxes of polystyrene or of an equivalent material, like for instance polyvinylchloride, covered with films that prevent the light radiations from interacting with the substances dissolved.